anatomy A small structure resembling a rootlet (such as a fibril of a nerve).

Roget 153: cause, origin, source, principle, element; occasioner^†, prime mover, primum mobile [Lat.]; vera causa [Lat.]; author etc. (producer) 164; mainspring; agent; leaven; groundwork, foundation etc. (support) 215.    spring, fountain, well, font; fountainhead, spring head, wellhead; fons et origo [Lat.], genesis; descent etc. (paternity) 166; remote cause; influence.    pivot, hinge, turning point, lever, crux, fulcrum; key; proximate cause, causa causans [Lat.]; straw that breaks the camel's back.    ground; reason, reason why; why and wherefore, rationale, occasion, derivation; final cause etc. (intention) 620; les dessous des cartes [Fr.]; undercurrents.    rudiment.    egg, germ, embryo, bud, root, radix radical, etymon, nucleus, seed, stem, stock, stirps, trunk, tap-root, gemmule^†, radicle, semen, sperm.    nest, cradle, nursery, womb, nidus, birthplace, hotbed.    causality, causation; origination; production etc. 161.    ... show more